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.. _mach_settings:
Mach can read settings in from a set of configuration files. These
configuration files are either named ``machrc`` or ``.machrc`` and
are specified by the bootstrap script. In mozilla-central, these files
can live in ``~/.mozbuild`` and/or ``topsrcdir``.
Settings can be specified anywhere, and used both by mach core or
individual commands.
Core Settings
These settings are implemented by mach core.
* alias - Create a command alias. This is useful if you want to alias a command to something else, optionally including some defaults. It can either be used to create an entire new command, or provide defaults for an existing one. For example:
.. parsed-literal::
mochitest = mochitest -f browser
browser-test = mochitest -f browser
Defining Settings
Settings need to be explicitly defined, along with their type,
otherwise mach will throw when trying to access them.
To define settings, use the :func:`~decorators.SettingsProvider`
decorator in an existing mach command module. E.g:
.. code-block:: python
from mach.decorators import SettingsProvider
from mozbuild.base import MachCommandBase
class ArbitraryClassName(MachCommandBase):
config_settings = [
('', 'string', "A helpful description"),
('foo.baz', 'int', "Another description", 0, {'choices': set([0,1,2])}),
``@SettingsProvider``'s must specify a variable called ``config_settings``
that returns a list of tuples. Alternatively, it can specify a function
called ``config_settings`` that returns a list of tuples.
Each tuple is of the form:
.. code-block:: python
('<section>.<option>', '<type>', '<description>', default, extra)
``type`` is a string and can be one of:
string, boolean, int, pos_int, path
``description`` is a string explaining how to define the settings and
where they get used. Descriptions should ideally be multi-line paragraphs
where the first line acts as a short description.
``default`` is optional, and provides a default value in case none was
specified by any of the configuration files.
``extra`` is also optional and is a dict containing additional key/value
pairs to add to the setting's metadata. The following keys may be specified
in the ``extra`` dict:
* ``choices`` - A set of allowed values for the setting.
Sometimes a section should allow arbitrarily defined options from the user, such
as the ``alias`` section mentioned above. To define a section like this, use ``*``
as the option name. For example:
.. parsed-literal::
('foo.*', 'string', 'desc')
This allows configuration files like this:
.. parsed-literal::
arbitrary1 = some string
arbitrary2 = some other string
Finding Settings
You can see which settings are available as well as their description and
expected values by running:
.. parsed-literal::
./mach settings # or
./mach settings --list
Accessing Settings
Now that the settings are defined and documented, they're accessible from
individual mach commands from the mach command context.
For example:
.. code-block:: python
from mach.decorators import (
from mozbuild.base import MachCommandBase
class ExampleSettings(object):
config_settings = [
('a.b', 'string', 'desc', 'default'),
('', 'string', 'desc',),
('foo.baz', 'int', 'desc', 0, {'choices': set([0,1,2])}),
@Command('command', category='misc',
description='Prints a setting')
def command(command_context):
settings = command_context._mach_context.settings
for option in